The disclosure generally relates to a USB control circuit and, more particularly, to a USB control circuit with built-in bypass function.
The USB hub device is a common data transmission equipment and utilized for converting and dispatching data between a USB host device and a USB peripheral device. The USB hub device includes an upstream port for connecting with the USB host device and a downstream port for connecting with the USB peripheral device.
The supplementary specification of the USB protocol has defined an On-the-Go (OTG) function, which allows a USB peripheral device supporting the OTG function (a.k.a. an OTG device) to selectively play the role of a USB host device or a USB peripheral device in different situations. Accordingly, the OTG device is categorized as a dual role device.
However, the devices to be connected to the upstream port and the downstream port of the conventional USB hub device are not swappable. Otherwise, data communication between the USB host device and the USB peripheral device cannot be conducted successfully through the conventional USB hub device. For example, when the OTG device is connected to the upstream port of the conventional USB hub device, the OTG device is only allowed to play the role of a USB host device, and not allowed to play the role of a USB peripheral device. On the other hand, when the OTG device is connected to the downstream port of the conventional USB hub device, the OTG device is only allowed to play the role of a USB peripheral device, and not allowed to play the role of a USB host device.
As a result, when two OTG devices are respectively connected to the upstream port and the downstream port of the conventional USB hub device, the roles of the two OTG devices are restricted and cannot be swapped.
It is apparent that the conventional USB hub device severely restricts the functions of the OTG devices, thereby reducing the usage flexibility of the OTG devices.